JP2003238138A - Silicon purification method and silicon purification apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon purification method and a silicon purification apparatus capable of efficiently purifying silicon. SOLUTION: The silicon refining apparatus 1 comprises a crucible 7, a raw material body 2 containing silicon and impurities in the crucible 7, a charging means 5 for charging a slag agent 3 for removing impurities, and a raw material body 2. An electromagnetic induction heating device 8 for heating the slag agent 3 to form the melt 6, a stirring member 9 for stirring the melt 6, and a gas outlet 33 as gas supply means are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a method and an apparatus for purifying silicon, and more particularly to a method and an apparatus for producing high-purity silicon for solar cells. is there.

[0002]

2. Description of the Related Art In recent years, the utilization of natural energy as an alternative energy for petroleum has attracted attention, and in particular, the utilization of solar energy by solar cells is expected to expand its utilization and spread as environmentally friendly energy. For this reason, it is important to reduce the cost of solar cells using the semiconductor photoelectric conversion principle, and particularly to reduce the cost of expensive silicon raw materials.
As a semiconductor material for a solar cell, a silicon material is predominant from the viewpoint of resource efficiency, environmental friendliness, high conversion efficiency, and the like. Expensive high-purity silicon for integrated circuits is used as the silicon material.

Since silicon for integrated circuit semiconductors requires extremely high purity, in the present manufacturing method, metal silicon having a purity of 98% or more obtained by reducing silica is used as silane (Si).
H ₄ ) or trichlorosilane (SiHCl ₃ ). By subjecting those gases to hydrogen reduction in a bell jar furnace, ultra-high-purity polycrystalline silicon called 11N is obtained. This method is costly due to the high energy used in the manufacturing process. It is said that silicon for solar cells is not required to have ultra-high purity as high as silicon for semiconductors, and conventionally, development of a refining technique for mass production from inexpensive metal silicon has been underway. One of the methods is solid-liquid distribution during solidification of heavy metal impurities such as iron, aluminum, titanium, boron, or phosphorus, which have an adverse effect on the performance (conversion efficiency) of solar cells, among the impurity elements in metallic silicon. There is a method of removing by unidirectional solidification by utilizing the fact that the ratio, that is, the segregation coefficient is small.

However, since the segregation coefficients of boron and phosphorus contained in silicon are about 0.8 and 0.35, respectively, which are very large, solidification segregation represented by the above-mentioned unidirectional solidification method was used. Purification methods cannot remove impurities to the level of purity required to manufacture solar cells.

Therefore, regarding the removal of phosphorus, the characteristic that the vapor pressure of phosphorus is high is utilized. For example, in Japanese Patent No. 2905353, the molten silicon is held under reduced pressure to bring phosphorus into the gas phase. The method of release is shown.

Regarding the removal of boron, Japanese Patent No. 2851
As disclosed in Japanese Patent No. 257,257, there is a method of introducing slag into molten silicon. In addition, Japanese Patent Laid-Open No. 2001-2001
Japanese Patent No. 58811 discloses a method of blowing a processing gas such as argon containing water vapor while stirring a molten silicon by using a rotating impeller or Lorentz force.
In either method, in principle, boron is removed from the molten silicon by forming boron in the oxide form by an oxidation reaction.

[0007]

The methods for refining silicon by metallurgical methods include the above-mentioned ones, but none of them has been commercially established due to cost problems. Taking the removal of boron as an example, in the method of introducing the slag containing CaO and SiO ₂ as the main components into the molten silicon as disclosed in Japanese Patent No. 2851257, the removal of boron into the slag with respect to the boron in the silicon is considered. The ratio of included boron, so-called distribution coefficient is 2-3
It is a degree. When metallic silicon originally containing about 10 ppm of boron is used as a raw material, slag several times as much as the amount of silicon is required to bring the boron concentration to about 0.3 ppm required for solar cells. It will be. Therefore, it is not realistic for commercial purposes. Further, in the slag treatment method, it takes several hours until impurities in silicon are taken into the slag and the concentration of impurities in the silicon and the slag reach equilibrium. Therefore, the throughput is poor. The reason for this poor processing speed is that slag generally has a larger specific gravity than silicon, so it precipitates in the lower part of the processing tank, and the contact interface with molten silicon cannot be increased. In other words, it is considered that the processing speed becomes slow because the reaction area is small.

According to the method disclosed in Japanese Patent Laid-Open No. 2001-58811, a process gas such as argon containing water vapor is blown in while stirring a molten metal of silicon by using a rotating impeller or Lorentz force. Since it is simple, it can be expected to reduce the manufacturing cost. However, processing 4
The content of boron is reduced from 7 ppm to 2 to 5 ppm by carrying out for 0 minutes, the reaction rate is not dramatically improved, and there is no prospect of commercialization.

Therefore, the present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to efficiently and inexpensively process an impurity element contained in a metal such as silicon. To remove and provide a silicon raw material for solar cells.

[0010]

A method for purifying silicon according to the present invention comprises: a raw material body containing silicon and impurities;
The method includes a step of preparing a melt containing an impurity removing agent for removing impurities, a step of stirring the melt, and a step of supplying a gas for removing impurities to the stirred melt.

According to the method for purifying silicon having such steps, the melt containing the impurity removing agent is stirred, and a gas for removing impurities is supplied into the melt during the stirring. Therefore, the gas supplied into the agitated melt is sheared into fine particles and efficiently dispersed in the molten silicon or the impurity removing agent. This results in gas,
The contact area of each of the three phases of the molten silicon and the impurity removing agent is increased. Therefore, the impurity removing agent can efficiently remove the impurities. Further, the melt is stirred and mixed, so that the impurity removing agent having a larger specific gravity than silicon is dispersed in silicon. for that reason,
The mixed state of the molten silicon, the processing gas, and the impurity removing agent is improved, and the respective contact areas are increased, so that impurities in the melt can be removed in a short time. Therefore, the silicon raw material for solar cells can be efficiently manufactured at low cost.

Further preferably, the step of preparing the melt comprises
It includes a step of preparing a melt containing a mixture of the raw material body and CaO containing SiO ₂ as a main component.

Further preferably, the step of supplying a gas to the melt includes a step of supplying a gas containing at least one selected from the group consisting of an inert gas, water vapor and carbon monoxide.

Further preferably, the impurity removing agent oxidizes and removes the impurities. The apparatus for purifying silicon according to the present invention comprises a container, a raw material body containing silicon and impurities, a charging means for charging an impurity removing agent for removing impurities into the container, and a raw material body and an impurity removing agent. A heating means for heating to form a melt, a first stirring means for stirring the melt, and a gas supply means for supplying a gas for removing impurities to the melt are provided.

In the silicon refining apparatus thus constructed, the heating means heats the raw material and the impurities to form a melt, and the melt is stirred by the first stirring means, and the stirring is performed. A gas for removing impurities can be supplied to the melt thus formed. Therefore, the gas is sheared and efficiently dispersed in the molten silicon or the impurity removing agent. As a result, the contact area of each of the three phases of gas, molten silicon and impurity removing agent increases. Therefore, the throughput can be improved. In addition, since the impurity removing agent having a larger specific gravity than silicon is stirred and dispersed, the mixed state of the molten silicon, the gas and the impurity removing agent is improved, and the contact area of each is increased, so that the impurities in the melt are Can be removed in a short time. Therefore, the silicon raw material for solar cells can be efficiently manufactured at low cost.

Further preferably, the first stirring means includes a rotating shaft and a blade member attached to the rotating shaft so as to be immersed in the melt and rotating together with the rotating shaft in the melt. In this case, by rotating the blade member, the melt is stirred more efficiently.

Also preferably, the gas supply means includes a gas ejection port provided in the blade member. In this case, since the blade member agitates the melt and the gas is supplied from the blade member, the gas is sheared and dispersed by the melt. As a result, the contact area between the gas, the impurity removing agent, and silicon is further increased, and the impurities can be efficiently removed.

Further preferably, the gas supply means includes a gas ejection port provided in a portion of the rotary shaft which is immersed in the melt. In this case, the gas ejection port can be easily formed by providing the rotation shaft with the gas ejection port.

Further preferably, the silicon refining device is
It further comprises a drive means for moving the rotating shaft in a direction in which the rotating shaft extends. In this case, the driving means drives the rotary shaft in the vertical direction, whereby the melt can be stirred more efficiently.

Also preferably, the apparatus for purifying silicon is
It further comprises a second stirring means immersed in the melt and performing an operation relatively different from that of the first stirring means. In this case, the melt can be stirred more efficiently by mixing the melt with the first stirring means and the second stirring means.

Further preferably, the first stirring means includes a magnetic field applying means for applying a magnetic field to the melt so that the Lorentz force acts on the ions in the melt. In this case, by applying a magnetic field and stirring the melt by Lorentz force, the melt can be rotated without mechanical operation.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a sectional view of a silicon refining apparatus according to Embodiment 1 of the present invention.
FIG. 2 is a perspective view of the stirring member 9. FIG. 3 is a perspective view of the stirring member 13.

Referring to FIG. 1, a first embodiment of the present invention
The silicon refining apparatus 1 according to the above is equipped with a crucible 7 as a container.
And a raw material body 2 containing silicon and impurities in the crucible 7.
And a slag agent 3 as an impurity removing agent for removing impurities
And charging means 5, an electromagnetic induction heating device 8 as a heating means for heating the raw material body 2 and the slag agent 3 to form the melt 6, and a first stirring means for stirring the melt 6. The stirring member 9 and the melt 6 are provided with a gas ejection port 33 as a gas supply means for supplying a gas for removing impurities.

The silicon refining apparatus 1 has a melting furnace 19. The electromagnetic induction heating device 8 is housed in the melting furnace 19. The electromagnetic induction heating device 8 is positioned so as to face the refractory material 15. Refractory material 15 is a protective crucible 14
Cover. The crucible 7 is housed in the protective crucible 14. The melt 6 is put in the crucible 7. The melt 6 includes a raw material body 2 composed of molten silicon and impurities, and a slag agent 3 as an impurity removing agent. Further, the gas 4 is dispersed in the melt 6.

A stirring member 13 as a second stirring means is provided so as to be immersed in the melt 6. Further, a stirring member 9 as a first stirring means is provided so as to be coaxial with the stirring member 13. A gas passage 11 is provided in the stirring member 9, and the gas passage 11 is connected to the gas ejection port 33. The stirring member 9 is connected to the driving means 12, and the driving means 12 moves the stirring member 9 in the vertical direction. The gas in the crucible 7 is drawn from the gas outlet 18 to the arrow 17
It is discharged in the direction indicated by.

As the raw material body 2, metallic silicon having a purity of about 98% which is widely used industrially is used. Other,
A slightly high-purity silicon raw material after purified by directional solidification,
A silicon material after dephosphorization (P), a silicon material obtained by mixing high-purity and low-purity silicon, or the like can also be used.

As the slag agent 3, calcium silicate (C
aSiO ₃ ) is used. This calcium silicate is brought into a molten state by heating the crucible 7 together with silicon as a raw material. The fact that slag (molten oxide) represented by calcium silicate absorbs boron in the raw material body 2 is disclosed in, for example, Japanese Patent No. 2851257. The melting point of calcium silicate is 1544 ° C, which is higher than the melting point of silicon, 1414 ° C. As a particularly important physical property value, the specific gravity of calcium silicate is about 2.5 to 2.6, which is larger than the specific gravity of silicon of 2.3 to 2.4. Furthermore, the viscosity of molten calcium silicate is about 1 Pa · s, which is overwhelmingly higher than the viscosity of molten silicon of 0.001 Pa · s.
From the relationship between the specific gravity and the viscosity, it is understood that it is difficult to sufficiently mix molten silicon and molten calcium silicate. The melt 6 contains the raw material body 2 and SiO ₂ as main components, and contains S
The slag agent 3 is a mixture of iO ₂ and CaO.

Where the effects of the present invention are expressed,
It goes without saying that it is not limited to calcium silicate. For example, the ratio of silicon oxide (SiO ₂ ) and calcium oxide (CaO) may be changed to achieve various purposes such as adjusting the melting point and the viscosity. Also,
Aluminum oxide (Al ₂ O ₃ ), magnesium oxide (M
Known additives such as gO), barium oxide (BaO), and calcium fluoride (CaF ₂ ) may be appropriately added. The ratio of the components of calcium silicate (CaSiO ₃ ) is CaO: SiO ₂ = 50: 50 (melting point 1544).
℃), so to enhance the function as an oxidant,
It is desirable that the proportion of SiO ₂ is high. However, Ca
From the phase diagram of the binary system of O: SiO ₂ , CaO: SiO ₂
= 35: 65 (melting point 1436 ° C.), if the ratio of SiO ₂ is increased, the melting point rises sharply. Specifically CaO:
If SiO ₂ = 25: 75 (mass ratio), the melting point is 17
It becomes 00 ° C. Therefore, it does not become molten slag. Since the wettability is poor in the solid state, the contact area with the molten silicon becomes small, which is not preferable. In order to lower the melting point, for example, aluminum oxide (A
1 ₂ O ₃ ), magnesium oxide (MgO), barium oxide (BaO), calcium fluoride (CaF ₂ ), lithium oxide (Li ₂ O) and the like may be added.

Of the calcium silicate constituting the slag agent, silicon oxide (SiO ₂ ) removes boron.
Specifically, silicon oxide (SiO ₂ ) is decomposed and the oxygen reacts with boron in the molten silicon to form B ₂ O ₃ (liquid). Further, it is considered that HBO ₂ (gas) is formed by the water vapor blown into the molten silicon and the impurities are removed from the molten silicon by the following formula.

B ₂ O ₃ (liquid) + H ₂ O (gas) → HBO ₂
(Gas) According to this formula, the concentration of impurities in the slag agent does not increase.
As the refining process proceeds, the ability to oxidize boron in molten silicon is lost.

Silicon oxide (SiO 2) is used as a slag agent.
₂ ) and calcium oxide (CaO), which is a mixture of calcium silicate, is used to lower the melting point of SiO ₂ which is an oxidant. In the present invention, SiO ₂ functioning as an oxidizing agent for oxidizing boron is added to molten silicon in a molten state. At this time, since the melting point of the simple substance of SiO ₂ is as high as 1713 ° C., the viscosity also becomes high. C
By combining with aO, the melting point is lowered and the viscosity is lowered. Therefore, it becomes easy to stir in the molten silicon. Further, the melting point and the viscosity can be lowered by adding the above-mentioned additives.

As the gas supplied into the melt, a gas other than steam gas (H ₂ O) can be used. As a gas for oxidizing boron, in addition to steam gas, an oxygen-based gas such as carbon monoxide gas (CO) can be used to oxidize boron. Alternatively, a halogen-based gas such as hydrochloric acid (HCl) may be used. As a result of these oxidizing boron, BO, B
Various boron oxides such as O ₃ or B ₂ O ₃ are formed.

To carry out the nitriding reaction, nitrogen gas, ammonia gas or the like may be supplied. In this case, a nitride such as BN is formed.

Referring to FIG. 2, the stirring member 9 includes a rotating shaft 31 extending in one direction, a gas passage 11 provided inside the rotating shaft 31, and a blade member attached to an end portion of the rotating shaft 31. 32 and. A gas ejection port 33 is provided at the end of the blade member 32. Each of the gas ejection ports 33 is connected to the gas passage 11, and the gas supplied from the gas passage 11 is discharged from the gas ejection port 33.

Referring to FIG. 3, the stirring member 13 includes a rotating shaft 41 having a through hole 42, a connecting member 43 attached to the rotating shaft 41, and a rotating shaft 4 attached to the connecting member 43.
1 and a leg portion 44 extending in the same direction.

The wall of the melting furnace 19 in FIG. 1 is made of stainless steel, and in the melting furnace 19, a graphite crucible 7 into which raw material silicon and calcium silicate are inserted and an electromagnetic induction heating device 8 are installed. Although the electromagnetic induction heating device 8 is used in this embodiment, a resistance heating device may be used.

In order to introduce a processing gas (gas) for removing impurities in the raw material body 2 into the melt 6, the gas passage 1
1, a rotary shaft 31 as a gas blowing pipe, and a rotary shaft 3
The gas ejection port 33 provided in the lower part of 1 is installed inside the melting furnace 19. A driving means 12 is attached to the upper part of the rotary shaft 31 in order to stir the melt 6 to make the bubbles fine and uniformly disperse them. The rotating shaft 31 and the gas ejection port 33 are rotatable. Further, in order to rotate the second stirring means (stirring member) 13 as a baffle plate for dispersing the molten slag in the melt 6, the rotating shaft 31 of the rotating shaft 31 is provided above the support shaft 13a in order to rotate the second stirring means 13 in the melt 6. Driving means (not shown) is provided separately from the driving means 12. In this way, the rotary shaft 31 and the support shaft 13a can be independently rotated.

In this embodiment, the melt 6 is stirred by the blade member 32 provided on the rotary shaft 31, but the method of stirring the melt 6 may be vertical / horizontal direction or circular direction. Alternatively, a rod-shaped or plate-shaped stirring jig for moving the blade member 32 in any direction such as to stir the melt 6 may be used separately. Further, the melt 6 may be rotated by rotating the crucible 7.

At the portion where the rotary shaft 31 penetrates the wall of the melting furnace 19, the hermeticity inside the melting furnace 19 is ensured, and
A seal mechanism 16 is provided for allowing the rotary shaft 31 to rotate. At the upper end of the rotary shaft 31, a blade member 32 is immersed in the melt 6 of the crucible 7 during processing, and before and after the processing, a driving means 12 as an elevating mechanism for pulling up the blade member 32 from the melt 6 is installed. Has been done.

The melting furnace 19 is filled with an inert gas atmosphere such as argon, and the crucible 7 is heated by the electromagnetic induction heating device 8. The temperature of the raw material silicon and calcium silicate rises due to electric heat from the crucible 7, and finally melts. The melt 6 thus formed is maintained at a predetermined processing temperature. At this stage, the molten silicon and molten calcium silicate are separated from each other. At this time, several grams of molten silicon is sampled as a sample for measuring the boron content in the pretreatment.

The processing gas is jetted from the gas jet port 33 through the gas passage 11, and the drive means 12 drives the rotary shaft 31.
And the blade member 32 is dipped in the melt 6. At this time, the introduction pressure of the processing gas is higher than the atmospheric pressure, and for example, is set to about 0.15 MPa to 0.3 MPa, so that the processing gas can be stably treated even in a melt mixed with a substance having a high viscosity such as molten calcium silicate. Can continue to squirt. In order to oxidize and remove boron dissolved in molten silicon, a mixed gas of argon and water vapor is used as gas 4 and melt 6
Introduced in. The amount of water vapor in the gas 4 was adjusted so that the dew point of the gas 4 was 20 to 90 ° C. by using a humidifier. This means that about 7 to 20% by volume of water vapor gas is contained with respect to the carrier gas of argon. Hydrogen gas may be appropriately added to the gas 4. The processing gas 4 is not limited to the steam-containing gas. The gas is appropriately selected depending on the type of reaction for removing impurities. For example, if it is an oxidation reaction, an oxygen-based gas such as carbon monoxide gas (CO) or a halogen-based gas such as hydrochloric acid (HCl) may be used. If it is a nitriding reaction, nitrogen gas or ammonia gas (NH ₃ ) may be supplied.

After lowering the blade member 32 below the melt 6, the blade member 32 is rotated by the driving means 12. The gas 4 ejected from the gas ejection port 33 is sheared by the rotating blade member 32 to be finely divided, and similarly, the blade member 3
The gas 4 is efficiently dispersed in the molten silicon and the slag agent 3 sheared by 2. This effect causes gas 4
JP 2001-58811 A discloses that the removal rate of boron increases when a medium such as calcium silicate is not added by increasing the contact area between the melt 6 and the melt 6. However, the present inventor discovered that the addition rate of calcium silicate markedly increased the processing rate of boron, and thus created the present invention. The principle is not clear, but it is considered as follows. By rotating the rotary shaft 31 and the blade member 32, even a substance having a high viscosity such as calcium silicate can be finely dispersed by shear stress. This, combined with the miniaturization and uniform dispersion of the bubbles of the processing gas, causes the three phases of the processing gas, the molten calcium silicate, and the molten silicon to be mixed very efficiently, and the contact area between the respective phases is significantly increased. In such a state, the boron oxidation formed by the conventionally known oxidation reaction between boron in molten silicon and steam of the processing gas and the oxidation reaction between boron in molten silicon and oxygen ions in molten calcium silicate. The matter is quickly incorporated into the molten calcium silicate. However, the boron incorporated in the molten calcium silicate reaches saturation at about twice the weight of boron contained in the same weight of molten silicon. The boron removal reaction should stop at some point. However, according to the method of the present invention, the boron removal reaction proceeded with the passage of time, so it is considered that there is a reaction in which the boron in the molten calcium silicate is released. This is because the boron in the molten calcium silicate reacts with the water vapor in the process gas and is released from the molten calcium silicate into the gas 4 or into the melt 6 as a boron-containing gas such as B ₂ O ₃ or BHO ₂ . It is considered to be a thing.

Thus, in order to enhance the reaction in the presence of molten slag, it is important to increase the reaction area by stirring.

After the treatment for a predetermined time, the rotating shaft 31 is raised by the elevating mechanism until the blade member 32 is located sufficiently above the surface of the melt 6. The melt 6 is allowed to stand for several minutes to sufficiently separate the molten silicon and the molten calcium silicate, and then several grams of the molten silicon is sampled to measure the boron content after the treatment as a measurement sample. The boron content is measured using a known ICP issuance analysis table.

An embodiment using the apparatus shown in FIGS. 1 to 3 will be described below. As a silicon raw material, in order to clearly show the purification effect, a mixture containing a raw material body 2 having a boron concentration of 7 ppm and the remainder being silicon and calcium silicate as a slag agent 3 was prepared. The mass ratio Si: CaSiO _{3 of} silicon and calcium silicate was set to 19: 1. 1 kg of this mixture was charged into the crucible 7 using the charging means 5. The inside of the melting furnace 19 was set to an atmospheric pressure argon gas atmosphere. The raw material silicon and calcium silicate were melted by heating the crucible 7 with the electromagnetic induction heating device 8 and kept at a temperature of 1550 ° C. Since the molten calcium silicate has a higher specific gravity than the molten silicon, it was deposited on the bottom of the crucible 7. The stirring member 9 was moved down by the drive means 12 until the gas ejection port 33 reached near the interface between the molten calcium silicate and the molten silicon. At the same time, the second stirring means (stirring member) 13 as a baffle plate was moved down to near the bottom of the crucible 7. The stirring means 9 was driven by the driving means 12 to drive the stirring member 9 at 600 rpm while jetting the gas 4 mixed so that the content of water vapor was about 3% by volume with respect to the argon gas at a flow rate of 1 liter / minute from the gas jet port 33. I rotated it. The support shaft 13a is moved in the opposite direction to the stirring member 9 by 200 rp.
It was rotated at m and treated for 1 hour. When the boron content after the treatment was measured, the boron concentration after the treatment was 0.2 ppm.

(Second Embodiment) FIG. 4 is a sectional view of a silicon refining apparatus according to a second embodiment of the present invention.
FIG. 5 is a sectional view taken along the line VV in FIG. Figure 4
Referring to FIG. 5 and FIG. 5, in the silicon refining device 1 according to the second embodiment of the present invention, the second stirring means (stirring member) 13 as the baffle plate does not rotate. Different from the silicon refining apparatus 1 shown. Although the stirring member 13 as the baffle plate is fixed, the stirring member 9 is driven, so that the stirring member 13 is immersed in the melt 6 as in the first embodiment, and serves as the first stirring means. The operation is relatively different from that of the stirring member 9.

As in the first embodiment, the boron concentration is 7p.
Raw material silicon adjusted to pm and calcium silicate were mixed at a weight ratio of 19: 1 to form a mixture. While the gas as the processing gas is ejected from the gas ejection port 33 at a flow rate of 3 liters / minute, the stirring means 9 is driven to 600 r by the driving means 12.
It was rotated at pm. The stirring member 13 is the stirring member 9 before processing.
At the same time, the melt 6 was impregnated. In the present embodiment, the stirring member 13 was fixed during the process. After the treatment for 1 hour, the boron content after the treatment was measured and found to be 0.4 ppm.

(Third Embodiment) FIG. 6 is a sectional view of a silicon refining apparatus according to a third embodiment of the present invention.
Referring to FIG. 6, in a silicon refining device 1 according to a third embodiment of the present invention, stirring member 9 is provided with four blade members 32. The blade member 32 has a plate shape. The gas ejection port 33 is provided at the lower end of the stirring member 9. In addition, in this embodiment, the second stirring means as a baffle plate is not provided. Others are the same as those in the first embodiment described above.

The raw material body 2 having a boron concentration of 7 ppm and the balance being silicon and calcium silicate in a mass ratio of 9: 1.
To form a mixture. Gas 4 with gas outlet 33
From the above, the stirring member 9 was rotated at 600 rpm by the driving means 12 while jetting at a flow rate of 3 l / min. In this embodiment, the molten silicon has a spiral shape so as to wind around the gas ejection port 33. After the treatment for 1 hour in this manner, the boron content after the treatment was measured.
It was 1.1 ppm.

FIG. 7 is a perspective view showing another example of the stirring member shown in FIG. The blade member 32 may be obliquely attached as shown in FIG. 7.

(Fourth Embodiment) FIG. 8 is a sectional view of a silicon refining apparatus according to a fourth embodiment of the present invention.
Referring to FIG. 8, a silicon refining device 1 according to a fourth embodiment of the present invention includes a coil 61 as a magnetic field applying means.
Have. An electromagnetic induction heating device 62 as a heating means is provided outside the coil 61. The coil 61 as the first stirring means applies a magnetic field to the melt 6 so that the Lorentz force acts on the ions in the melt 6. This allows
The melt 6 is agitated. The silicon refining apparatus 1 has a plurality of gas blowing pipes 10.

The silicon refining apparatus according to the fourth embodiment of the present invention thus constructed has the same effects as those of the first to third embodiments.

Comparative Example 1 Silicon was refined under the same conditions as in Embodiment 1 except that calcium silicate was not added. After the treatment for 1 hour, the boron content after the treatment was measured and found to be 2.4 ppm.

Comparative Example 2 As shown in FIG. 9, silicon was refined in the same manner as in Example 1 except that the second stirring means was not used and the gas blowing pipe 10 was not rotated. After the treatment for 1 hour, the boron content after the treatment was measured and found to be 2.1 ppm.

The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

[0057]

According to the method according to the present invention, the second patent
The ability to remove boron from molten silicon is dramatically improved by adding a very small amount of slag as compared to the conventional technique disclosed in Japanese Patent No. 851257. The place to which the present invention is applied is not limited to this embodiment. For example, the amount of calcium silicate added, the flow rate of the processing gas, the number of revolutions of the gas injection pipe and the baffle plate, etc. are processed. It should be appropriately selected depending on the amount of raw material silicon or the shape of the crucible.

[Brief description of drawings]

FIG. 1 is a sectional view of a silicon refining device according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a stirring member 9.

FIG. 3 is a perspective view of a stirring member 13.

FIG. 4 is a sectional view of a silicon refining device according to a second embodiment of the present invention.

5 is a cross-sectional view taken along the line VV in FIG.

FIG. 6 is a sectional view of a silicon refining device according to a third embodiment of the present invention.

FIG. 7 is a perspective view showing another example of the stirring member shown in FIG.

FIG. 8 is a sectional view of a silicon refining device according to a fourth embodiment of the present invention.

9 is a cross-sectional view of a silicon refining apparatus according to Comparative Example 2. FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Silicon refining apparatus, 2 Silicon, 3 slag agent, 4 melts, 5 charging means, 7 crucibles, 9 stirring members, 11 gas passages, 13 stirring members, 31 rotating shafts,
32 blade members, 33 gas ejection port.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoshi Hayakawa             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F-term (reference) 4G072 AA01 GG01 GG03 GG04 GG05                       HH01 MM08 UU02

Claims (11)

[Claims] 1. A step of preparing a melt containing a raw material body containing silicon and impurities, and an impurity removing agent for removing the impurities, a step of stirring the melt, and the melt being stirred. And a step of supplying a gas for removing the impurities. 2. The purification of silicon according to claim 1, wherein the step of preparing the melt includes the step of preparing a melt containing a mixture of the raw material body and CaO containing SiO ₂ as a main component. Method. 3. The step of supplying the gas to the melt comprises:
The method for purifying silicon according to claim 1 or 2, comprising a step of supplying a gas containing at least one selected from the group consisting of an inert gas, water vapor and carbon monoxide. 4. The method for purifying silicon according to claim 1, wherein the impurity removing agent oxidizes and removes the impurities. 5. A container, a charging means for charging a raw material body containing silicon and impurities, and an impurity removing agent for removing the impurities into the container, and heating the raw material body and the impurity removing agent. A device for purifying silicon, comprising: a heating unit that forms a melt by heating; a first stirring unit that stirs the melt; and a gas supply unit that supplies a gas that removes the impurities to the melt. 6. The first stirring means includes a rotating shaft, and a blade member attached to the rotating shaft so as to be immersed in the melt and rotating together with the rotating shaft in the melt.
The apparatus for purifying silicon according to claim 5. 7. The apparatus for purifying silicon according to claim 6, wherein the gas supply unit includes a gas ejection port provided in the blade member. 8. The apparatus for purifying silicon according to claim 6, wherein the gas supply unit includes a gas ejection port provided in a portion of the rotary shaft that is immersed in the melt. 9. The silicon purifying apparatus according to claim 5, further comprising a driving unit that moves the rotating shaft in a direction in which the rotating shaft extends. 10. The second stirring means according to claim 5, further comprising a second stirring means that is immersed in the melt and performs a different operation relative to the first stirring means. Silicon refining equipment. 11. The silicon purifying method according to claim 5, wherein the first stirring means includes magnetic field applying means for applying a magnetic field to the melt so that Lorentz force acts on ions in the melt. apparatus.